How do I capture currently playing audio from another application in Rust?

Question

I want to capture the audio playing in another application e.g Chrome in my Rust project - to build an audio visualizer.

I have tried the cpal crate and I could record audio from the microphone and save it but I can't find any way to record audio from another source like Chrome.

Platform: Linux, Pipewire and Alsa

Answer 1

I found that you can use the alsa rust libray and hound crate to save the wav file.

Also, in pavucontrol - a gui application to control Pulseaudio, when you run the following program, make sure to change the device in the recording tab for your application to the speaker.

An example to capture 10 seconds of audio and save it:

// Adapted from alsa-rs github examples
use alsa::pcm::*;
use alsa::{Direction, Error, ValueOr};
use hound::{SampleFormat, WavWriter};

fn start_capture(device: &str) -> Result<PCM, Error> {
    let pcm = PCM::new(device, Direction::Capture, false)?;
    {
        // For this example, we assume 44100Hz, one channel, 16 bit audio.
        let hwp = HwParams::any(&pcm)?;
        hwp.set_channels(1)?;
        hwp.set_rate(44100, ValueOr::Nearest)?;
        hwp.set_format(Format::s16())?;
        hwp.set_access(Access::RWInterleaved)?;
        pcm.hw_params(&hwp)?;
    }
    pcm.start()?;
    Ok(pcm)
}

fn read(pcm: &PCM) {
    let io = pcm.io_i16().unwrap();

    let num_samples = 44100 * 10;
    let mut buffer = vec![0i16; num_samples];
    for i in 0..num_samples {
        let sample = io.readi(&mut buffer[i..i + 1]).unwrap();
        if sample == 0 {
            break;
        }
    }

    let spec = hound::WavSpec {
        channels: 1,
        sample_rate: 44100,
        bits_per_sample: 16,
        sample_format: SampleFormat::Int,
    };
    let mut writer = WavWriter::create("output3.wav", spec).unwrap();
    for sample in buffer {
        writer.write_sample(sample).unwrap();
    }
}

fn main() {

    let capture = start_capture("default").unwrap();
    read(&capture);
}